> 1/8/04 8:50 AM, Oliver Schad escribio:
> > Am Mittwoch, 7. Januar 2004 23:05 schrieb mir Mark Hurst:
> >> It's much better to have a firewall than just have ports not open.
> >> Even though a port is not open it can reveal the presence of your
> >> machine by the manner in which the IP stack responds to a connection
> >> attempt. Using a firewall you can drop those packets, making all
> >> your closed ports invisible.
> >
> > If you want to invisible, the next router to you have to send an ICMP
> > packet with "host unreachable". If you say nothing anybody with some
> > brain between his ears knows there is a very intelligent guy that
> > want to be invisible.
>
> AFAIK they appear as "filtered",that's the difference between a closed
> and a filtered port. The first responds with a "negative", the second
> doesn't respond. Am I wrong?

That's right. But no answer means there is somebody who doesn't answer.
Only if the last router before the target says "Hey, there is nobody",
then there is nobody (or there is an really intelligent guy, that wants
to hide his host).
To hide a host is always very stupid, why should you do this? There is no
advantage. If you "hide" your computer an attacker knows there is an
stupid guy who doesn't know anything about network security.
mfg
Oli
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